LOS ANGELES, CA, USA
N174UA
BOEING 747-422
THE CREW NOTED THAT THE NOSE AND MAIN BODY GEAR INDICATED UP AND LOCKED AFTER NORMAL GEAR EXTENSION. THE CREW USED THE ALT GEAR EXTENSION PROCEDURE, WHICH WAS UNSUCCESSFUL. THE AIRCRAFT LANDED WITH THE NOSE AND MAIN BODY GEAR RETRACTED WHEN THE FLIGHT REACHED THE MIN FUEL STATE. EXAM OF THE AIRCRAFT REVEALED THAT THE SELECTOR VALVE FOR THE AFFECTED GEAR WAS IN THE UP AND LOCKED POSITION, AND THE BOLT WHICH CONNECTS THE VALVE ARM TO THE COCKPIT CONTROL CABLE SYSTEM WAS MISSING. THE BOLT FOR WING GEAR SELECTOR VALVE ARM WAS FOUND PARTIALLY BACKED OUT; THE NUT AND COTTER PIN WERE MISSING. THE AIRCRAFT WAS DELIVERED TO UNITED IN JAN OF 1990 AND HAD 2,952 FLT HRS AND 402 CYCLES. DETAILED REVIEW OF THE MAINT RECORDS PROVED THAT UNITED HAD NOT PERFORMED ANY MAINT ON THE LANDING GEAR SYSTEM. A SECOND ALT GEAR EXTENSION PROCEDURE INVOLVING DE-ENERGIZING THE HYDRAULIC SYSTEM FOR THE AFFECTED GEAR IS NOT PUBLISHED IN THE CREW MANUALS, TAUGHT DURING INITIAL TRAINING, NOR AVAILABLE ON ANY CHECKLIST.
THE FAILURE OF THE MANUFACTURER TO ENSURE THAT THE LANDING GEAR SELECTOR VALVES AND THEIR ASSOCIATED DRUM LINK ASSEMBLIES WERE PROPERLY INSTALLED PRIOR TO DELIVERY OF THE AIRCRAFT. A FACTOR IN THE ACCIDENT WAS THE LACK OF INFORMATION AVAILABLE TO THE CREW CONCERNING THE SECONDARY ALTERNATE GEAR EXTENSION PROCDURE.
Source: NTSB Aviation Accident Database
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